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A Tale of Two Calendars

This time every year, the Internet is abuzz with articles expounding myths regarding the origins of the Easter celebration, and other articles debunking these myths. I’m not going to address this topic (perhaps in a future article…), but I do want to address a myth or urban legend popular in Orthodoxy and much less covered (at least outside of Orthodox blogs): that Easter (or Pascha as we typically call it) must fall after Jewish Passover, and that those rascally Roman Catholics removed that requirement, which is why (most) Orthodox Christians celebrate it on a later date most years.

Now it’s certainly true that the vast majority of Orthodox Christians do typically celebrate Easter one or more weeks after the West (Catholic/Protestant)… a fact even subtly lampooned in an episode of The Simpsons, captured in the image above. But that the reason has anything to do with Passover is simply false.

Why would the Christian Church have their holiest holy day determined by another religion? What if all the Jews converted to Christianity? Would we maintain the Jewish calendar just so we can calculate the date of Pascha? Of course Passover is not necessary to determine the date of Easter.

So what is the reason for the difference? Well, to understand that we have to talk about calendars and history. We’ll also get into why some Orthodox Christians celebrate Christmas in January.

As person in the 21st Century, you probably take for granted the fact that the whole world seems to use the same calendar. March is March, whether you spell it Marzo or März. Other calendar systems only ever seem to be discussed with regard to exotic ancient civilizations and potential end-of-the-world scenarios, such as the Mayan calendar silliness from a few years ago. What you may not realize is that a standard global calendar is a pretty modern thing. In ancient and even not-so-ancient times, diversity was the rule not the exception. Different countries/civilizations had their own calendars and dating systems. Even within the Roman Empire, which used a standard Roman calendar, the year would vary by region! (The BC/AD system we use today came about some 800 years after Christ.) The Jews also had their own calendar, which is based on the lunar cycle instead of the solar system we are familiar with.

The civil calendar used by virtually every government in the world today is called the Gregorian calendar, named after the Pope who promulgated it in the Catholic Church in the 16th Century— Gregory XIII. It was originally only used by Catholic countries; England, for example, had already become Protestant and didn’t adopt it for some time later.

It was created to address inaccuracies between its predecessor, the Julian calendar (named after Julius Caesar but actually created by Caesar Augustus in the form we know it) and the actual astronomical year. The year was too long under the Julian calendar, so the calendar had gotten pretty out of sync with the astronomy. Of specific concern was the vernal equinox used to calculate Easter. But let’s backtrack a little and discuss the Roman calendar and how it evolved over the centuries. (We’ll also learn why February only has 28 days, and why it gets the Leap Day.)

The legendary first king and namesake of Rome, Romulus, is accredited with creating the first Roman calendar, around 753 BC. It looked like this:

Martius — 31 days
Aprilis — 30 days
Maius — 31 days
Iunius — 30 days
Quintilis — 31 days
Sextilis — 30 days
September — 30 days
October — 31 days
November — 30 days
December — 30 days

Definitely recognizable almost 3,000 years later, even if it is only 10 months long. Well, the next king of Rome, Numa Pompilius, apparently changed things up a bit:

Martius — 31 days
Aprilis — 29 days
Maius — 31 days
Iunius — 29 days
Quintilis — 31 days
Sextilis — 29 days
September — 29 days
October — 31 days
November — 29 days
December — 29 days
Ianuarius — 29 days
Februarius — 28 days (23 or 24 days in leap year)
Intercalarius — 0 days (27 days in leap year)

Numa deleted one day from all the 30-day months, and added Ianuaris and Februarius (January and February) to the end of the year, because under the old calendar there were only 304 days… after December 29 they would wait some 60-odd days until their astronomers determined it was time to start the new year again, which obviously wasn’t a very good system. The intercalarius wasn’t exactly a month, but a set of days added after February about every other year, in order to keep the seasons from getting too out of sync (which, as we will see, is the problem that drives all calendar updates.) This is the genesis of the leap year.

Fast forward a few centuries to around 450 BC, and we find that Ianuarius and Februarius are now considered the first and second month (as they are today), which makes the names of Quintilus and Sextilis kind of silly, since they come from the words for five and six.

Another unfortunate situation was that since there was no fixed rule for leap years, they could occur whenever it was decided that they should. This was abused, and by the time of Julius Caesar, the months were completely out of whack with the seasons.

In 45 BC, Julius Caesar solved this by creating the first fixed rules for determining leap years. He set a regular pattern of alternating between 31 and 30 day months. He also removed the intercalary month, replacing it with a single leap day, which is tacked on to the end of February because the intercalary month happened after February. He also added 3 months to the year on a one-time basis, in order to allow the seasons to catch up. So the calendar looked like this:

Ianuarius — 31 days
Februarius — 29 days (30 days in leap year)
Martius — 31 days
Aprilis — 30 days
Maius — 31 days
Iunius — 30 days
Quintilis — 31 days
Sextilis — 30 days
September — 31 days
October — 30 days
November — 31 days
December — 30 days

The leap year was fixed to every 4 years, but due to a counting error, it was actually implemented as every 3 years.

Julius Caesar didn’t get to enjoy his calendar, since he was murdered infamously on the Ides of March the following year. His successor, Augustus, picked up the calendar reforming torch, making the modifications that became known as the Julian calendar, after his predecessor. He changed the leap year to the proper 4 year cycle, and renamed the now-misnamed months of Quintilis and Sextilis after himself and Julius: Quintilis became Iulius (July) and Sextilis became Augustus (August.) The only problem was that the current Caesar’s month, Augustus, only had 30 days–one fewer than the month named for his predecessor. Considering this an outrage to his honor, Augustus took one day from February and added it to August, so that they would both have 31 days. This left February with only 28 days, a situation that endures until today.

The astronomical year is 365.2422 days long. With Augustus’ 4-year leap cycle, the average year was 365.25 days long. Pretty close, right? Well, not really, over a long enough span of time. That little difference comes to one full day every 128 years, or about 3 days every 400 years. By the 1500s, that came to a drift of 10 days. Today that drift is 13 days, and will be 14 days in the year 2100. That’s enough to start noticing the problem. The holidays became noticeably misaligned with the seasons.

Enter Pope Gregory XIII. To solve this, he did two things: removed 10 days from October in the year 1582, and changed the leap year rules so that years ending in 00 are only leap years if evenly divisible by 400. That means there would be 3 fewer days every 400 years, giving the average year a length of 365.2425 days, compared to the actual 356.2422. This means it will take 3,333 years for the calendar to drift one day, effectively solving that problem.

How October looked in 1582.

(Interestingly, in the 1920s, the Greek Orthodox Church proposed a leap year calculation that would solve even that drift by dropping 7 leap years every 900 years, but it has never been implemented.)

Pope Gregory also standardized the New Year’s Day (the day that the year is incremented) to January 1st. Prior to this, that day would vary from nation to nation. In the Byzantine Empire, that day was September 1st, which is why to this day the Church new year is on September 1 in the Byzantine Rite (Orthodox and Eastern Catholic Churches.)

Because the Roman Empire had included all of Europe and beyond at one point or another, the Julian calendar was pretty ubiquitous, at least in Europe. Most of the Catholic world–Poland, Italy, Portugal, and Spain–adopted the Gregorian calendar reforms immediately. Other Catholic countries like France followed shortly thereafter. The Protestant world was much slower to adopt them, creating a situation where different dates and years were recorded. Often both would be listed on documents. In the New World, Spanish and French colonies would use the new calendar system, while the British colonies maintained the older calendar. But eventually the new calendar won the support of governments worldwide. Among the last holdouts, Russia switched in 1918 and Turkey adopted it in 1927, both less than 100 years ago. (Alaska switched when it was purchased by the United States, but had the unique experience of not only losing days, but of repeating one day twice, because the International Date Line was shifted with the purchase, from being on the east side of Alaska prior, to the west side–in both cases in order to keep Alaska on the same day as its mother country.)

Well, just because the civil governments of Orthodox countries–such as Greece, Russia, and Yugoslavia–adopted the Gregorian calendar, that didn’t mean the Church was going to. Today, only one Orthodox Church has actually adopted the Gregorian Calendar: the Orthodox Church of Finland. However, quite a few churches eventually adopted what is called the ‘Revised Julian’ Calendar for fixed feasts. (The Julian calendar is still in use civilly on Mt. Athos (as well as liturgically of course) and by the Berber people of Northern Africa. Also, Ethiopia uses the Alexandrian Calendar, which is based on the Julian calendar.)

So, because of that 13 day drift, the Orthodox churches that use the Julian or “Old Calendar” celebrate the fixed feasts 13 days after those on the Gregorian or Revised Julian Calendars—but they still celebrate them on the same calendar day, e.g. December 25th for Christmas. It’s just that December 25th on the Julian calendar currently aligns with Jan 7 on the Gregorian. This is why in Russia and other countries, Christmas is celebrated in January (from the Gregorian perspective, anyway.)

Those Orthodox Churches that are on what is often called the “New Calendar” or “New Style,” (the Churches of Constantinople, Alexandria, Antioch, Greece (but not Mt. Athos), Cyprus, Romania, Poland, Bulgaria, and the Orthodox Church in America, except in Alaska) celebrate the fixed feasts on the same days as the Gregorian churches (Roman Catholic and Protestant), in accordance with the civil calendar that everybody uses, however Pascha is celebrated with the rest of the Orthodox. What they did in creating the Revised Julian calendar was remove 13 days from October the year it was adopted to sync up the dates, but specified that the vernal equinox used for the Paschalion or Computus (the determination of the date of Easter) would be that of the original Julian calendar.

So back to the calculation of Easter. In the early church, again diversity was the norm, even in determining the date of Easter. Some groups believed it should always be tied to the 14th day of the Jewish month of Nisan, regardless of the day of the week. Others thought it should always be on a Sunday, with various methods to determine which one. However, the date for Pascha has been completely divorced from Passover and the Jewish calendar since the formula was standardized at the First Council of Nicea. That Ecumenical Council set the calculation as the Sunday after the 14th day of the first lunar month of spring, which essentially boils down to the Sunday after the full moon after northern hemisphere’s vernal equinox. However, the equinox and full moon weren’t to be determined astronomically or by calculation; the equinox was fixed to March 21, and the new and full moons are called the ecclesiastical new and full moon and based on a complicated 19 year cycle of lunar months called the Metonic cycle.

(Note: The formula used clearly is derived from the date of Passover, but it doesn’t explicitly mention Passover, probably because in Orthodox Christian thought, the Jews should all become Orthodox–the New Israel being the Church–and Judaism as a separate religion should cease to exist. But using a lunar calendar, albeit a different one, and choosing the Sunday after the full moon, which is defined as the 14th day of the lunar month, in the spring month, is tantamount to saying the Sunday after 14 Nisan… the start of Passover. But it was set in such a way to be completely independent of what the Jews do, and in fact, the Jewish calendar has changed over the centuries. At times different Jews have even used different calendars. But most importantly, the change made by the Catholic Church had nothing to do with removing a requirement, but rather the difference is a result of the fact that the vernal equinox was set to a fixed day on the solar calendar.)

Despite a popular but misinformed narrative within Orthodoxy, the Catholic Church never changed the Computus of the First Ecumenical Council. They merely calculate the equinox as March 21 according to the Gregorian calendar, which is currently 13 days prior to March 21 on the Julian, which can therefore put the calculation of the ecclesiastical moons quite of sync (but not always) resulting in a different, earlier date of Pascha. It also has a side effect of making it possible that Easter is celebrated before Jewish Passover, but as previously noted, there is NO requirement that Easter follow Jewish Passover in the Computus that is used by both churches.

It’s supposed to be on the first Sunday after the first full moon after the spring equinox. But many centuries ago, we devised predictive mathematical cycles that predicted when the equinox and full moon would be. They were very accurate, but over time, those predictions drifted away from what was happening in the sky. We’ve never updated our tables. In the 16th century, the West did.

And there you have it. You probably now know more about calendars than you ever wanted to.

8 thoughts on “A Tale of Two Calendars”

I wonder whether this statement is accurate: “Despite a popular but misinformed narrative within Orthodoxy, the Catholic Church never changed the Computus of the First Ecumenical Council.” I’m doubtful because, when I use the tables in the 1928 Book of Common Prayer (Anglican) to compute the date of the ecclesiastical full moon immediately following 21 March 2016, I get 23 March – which happens to be the date of the actual full moon. The next ecclesiastical full moon, the one following Julian 21 March 2016, would then be 22 April. The Sunday following that full moon is 24 April. So, using this Western computation, Orthodox Easter should fall on 24 April this year. But, in fact, it’s 1 May.

As far as I know, the Anglicans always celebrate Easter on the same date as the Catholic Church, so I suppose the Anglican computational scheme is the same as the Catholic. But the Orthodox appear to use a different method for computing the date of the full moon.

The key pages are linked here: http://justus.anglican.org/resources/bcp/1928/Calendar&Tables_1928.pdf . To compute the date of Easter, one follows the instructions in the paragraph entitled, “TO FIND THE DATE OF EASTER DAY.” First, calculate the Golden Number for the year. With the Golden Number, go back a few pages to the section of the Calendar between 20 March and 18 April. The date the Golden Number lines up with is the date of the Paschal Full Moon for that year.

So, following the instructions, we add one to 2016, then divide by 19. The remainder is 3, which is the Golden Number for 2016. Go to the section of the Calendar between 20 March and 18 April, and find that the 3 in the first column lines up with 23 March, the computed date of the full moon.

(The Dominical or Sunday letter calculation simply allows someone without access to a calendar to determine the dates Sunday falls on.)

Yes, I would think so generally. There is a 30-something day window in which the feast can take place. I believe that the Julian version of that window must shift by 1 day against the Gregorian calendar every 128 years. However, since it just moves the earliest and latest dates, it will take many of those 128-year cycles before the overlap goes away.

Note I’m just deducing this answer from my understanding of the facts. I don’t really know for sure. But note that given the formula, the earliest Easter/Pascha could ever be is March 22, which is 13 days earlier Gregorian than Julian, a gap that has been increasing, so we can see right there that the possible dates have indeed been shifting. However, most years the date falls somewhere in the middle of the possible range, so it’s not as noticeable. It would be interesting to create a scatter plot of both Easter dates each year since the Gregorian calendar was invented.